Patellar instability treated with distal femoral osteotomy

Patellar instability can cause significant disability in both pediatric and adult patients, and it is associated with several factors including genu valgum. In this study, we describe the role of a lateral opening wedge distal femoral osteotomy (DFO) combined with lateral retinacular release in addressing genu valgum with associated patellar instability. The rationale for this approach is to medialize the patellar tendon insertion and decrease the Q angle with DFO.

A consecutive series of patients were studied, and our outcomes of interest included improvements in radiographic measures and patient outcomes. Radiographic improvement was assessed using patella congruency angle (PCA), mechanical axis deviation (MAD), and lateral distal femoral angle (LDFA). Patient outcomes were assessed using Oxford Knee scores, KOOS-PS scores, VAS pain scores, and Kujala scores.

We studied eight patients (10 knees) that underwent a lateral opening wedge DFO for genu valgum and patellar instability. Mean follow-up duration was 27 months. PCA improved from 30.4° lateral preoperatively to 5.7° lateral postoperatively (p=0.016). Similarly, MAD improved from 33.1mm lateral to 6.5mm medial, and LDFA improved from 82.4° to 92.7° after surgery (p=0.002). There were significant improvements in VAS pain and Kujala scores after surgery (p<0.05), and a trend towards improvement in KOOS-PS scores (p=0.14). The mean Oxford Knee score at follow-up was 36.25.

There is an important relationship between mechanical alignment and patellar instability. Lateral opening wedge DFO is an effective treatment for patellar instability in patients with genu valgum.